The invention describes a cone-style globe valve used for throttling of fluid or gases in applications typically found in the chemical, food or climate control applications using modulation valves to finely adjust the flow of fluid following signals from computerized control systems.
State of the art globe style control valves have been in use for centuries and comprise mainly a housing having an inlet and an outlet port, a central orifice connecting the ports and a vertically movable plug capable of selectively restricting the flow of fluid through the orifice. Such globe style control valves have to meet basic requirements besides reasonable cost such as meeting shut-off, an acceptable flow characteristic, low actuating forces and dynamic stability.
This invention constitutes an improvement over the current state of the art in that the design offers fewer parts, resulting in lower manufacturing cost, and greatly reducing force requirements enabling the use of smaller actuating devices for a given valve size, thereby again reducing cost and overall dimensions. In addition, the invention offers increased flow capacity per given orifice size. In contrast to conventional globe valves having single orifices, the invention offers two orifices in succession which can be closed simultaneously thereby substantially reducing the chances of fluid leaking across the valve. In contrast to typically solid valve plugs, the invention features a hollowed plug allowing fluid to pass fault the bottom of the plug to the top thereby greatly reducing forces required to move the plug against high fluid pressures.
Finally, the invention has greatly reduced seating surfaces areas. This enables better shut-off against high fluid pressures.
The purpose of an automatic process control valve is to vary the rate of flow in order to meet the demands of a process control system, such as controlling temperature. Such control can be done two ways:
1. By the variation of the flow area in a valve, and
2. By a variation of the hydraulic resistance in a valve passage.
One can define a flow coefficient FC of a valve as:FC=A×Cc×Hy/K0.5 at a give valve travel.Here, A=the flow area, Cc is a contraction coefficient, Hy=a hydraulic coefficient, and K is the velocity head loss coefficient.Good control valves demand that FC should increase exponentially with travel and that the ratio between FC at maximum travel to minimum travel should at least be thirty to one.
The current invention can accomplish such demands in contrast to prior art devices such as TRIADOU (U.S. Pat. No. 2,364,491). The device by Triadou has only a limited flow capacity since the flow area is defined only by the cone travel multiplied by the tangents of halfe of the cone angle. Furthermore, since the fluid resistance of his circular flow path (see FIG. 6) is constant, FC can only vary with travel; hence there is a linear characteristic (see FIG. 6-a). It offers only two identical and smooth flow paths encouraging cavitation and other un-desirable fluidic phenomenon.
There are so-called plug valves consisting of a housing having two opposed ports where the housing is centrally intersected by a horizontal opening having a conical shape and holding therein a rotatable cone having a horizontal opening aligning after every ninety degree rotation with the opposed ports in order to pass fluid. Such valves are almost exclusively used for the closure of pipes. The rotable cone exhibit a high degree of rotary friction requiring powerful rotary actuators for opening or closing such valves. This type of valve is un-suitable for modulating control since the high friction creates a hysteresis effect, which is very detrimental for stable control. Furthermore, the circular flow paths create very little hydraulic friction and therefore are not suited for pressure reduction.
The fact that the invented cone separates immediately from a similarly shaped conical opening in a housing upon lift-off, eliminates the undesirable friction exhibited by the aforementioned plug valves. Furthermore, a drain opening is provided connecting the housing interior between two ports to the outside, the valve thus being able to evacuate any fluid leakage from the upstream orifice before fluid is able to affect the downstream orifice when the valve is in the closed position. Thus, the invention could serve as a “block and bleed” device. These and other novel features may be gleaned from the following description.